Method and computer program product for evaluation of data recorded by measuring instruments

ABSTRACT

The invention describes a method and computer program product for the evaluation of data recorded by measuring instruments, which is particularly applicable to the precise localization of non-reflecting marks on a reflecting medium by means of a light-sensitive receiver and can be especially applied in precision positioning devices. The method comprises a first step in which data are recorded from a sensor on a measuring instrument with a minimized or extinguished measured signal and which is stored as a dark curve, a second step in which data of a normalized measured signal are recorded and stored as a reference curve, and a third step in which data for the current measurement are recorded and stored as a characteristic curve; the characteristic curve is then purged of errors caused by the measuring instrument by comparison against the dark curve or reference curve and normalized and the characteristic curve thus treated is stored as the target curve, and finally the target curve is evaluated for various values of the measured signal. The computer program product can be loaded directly into the internal memory of a computer and comprises software code sections, with which the above described method may be carried out when the product is running on a computer.

[0001] The invention concerns a method and a computer program productfor the evaluation of data recorded by measuring instruments, which areparticularly applicable to the precise localization of non-reflectingmarks on a reflecting medium by means of a light-sensitive receiver andcan be especially applied in precision positioning devices.

[0002] In signal processing, a plurality of methods exist for detectingedges or points in a signal curve. For the most part these containcomplicated processing instructions, which cause problems inimplementation on a microcomputer system with limited resources.

[0003] In addition, these methods permit only the determination of therelative position of marks since the detected signals are evaluated inthe receiver plane. Positions of several non-reflecting marks on areflecting medium can in fact be determined relative to one another withsufficient precision; the absolute position of the marks, however,previously could not be determined with high precision directly from the(optical) measured signals that were available.

[0004] The object of the present invention is to eliminate thedisadvantages of the known evaluation methods and to provide anoptimized method for the exact localization of a signal (point).

[0005] This object is solved according to the invention by the featuresin the characterizing part of claims 1, 6 and 7 in conjunction with thefeatures in the preamble. Appropriate configurations of the inventionare contained in the subclaims.

[0006] A particular advantage of the invention lies in the fact that inthe method for the evaluation of data recorded by measuring instruments,in a first step, the data supplied by the sensor(s) of the measuringinstrument(s) with a minimized or extinguished measured signal arerecorded and stored as a dark curve; in a second step, data of anormalized measured signal are recorded and stored as a reference curve;in a third step, the data of the current measurement are recorded andare stored as a characteristic curve 6; then the characteristic curve 6is purged of errors caused by the measuring instrument by comparisonwith the dark curve and/or the reference curve and/or is normalized; andthe thus-treated characteristic curve is stored as the target curve andfinally the target curve is evaluated for different values of themeasured signal.

[0007] The computer program product for the evaluation of data recordedby measuring instruments is characterized in that it can be loadeddirectly into the internal memory of a digital computer and comprisessoftware code sections with which the steps according to claim 1 can becarried out when the product is running on a computer.

[0008] Another advantage of the computer program product lies in thefact that it is stored on at least one medium suitable for computers andcomprises the following: computer-readable program means, which cause acomputer and/or a microcontroller to detect and to store data recordedby a measuring instrument; computer-readable program means, which causea computer and/or a microcontroller to compare the detected and storeddata with one another to purge these [data] of errors and/or tonormalize the data. The method according to the invention makes itpossible to achieve the localization of a mark with high precision andwith minimal technical expenditure. For this purpose, the followingsteps are conducted: preparation (calibration), normalization,evaluation of the target curve for special values of the measured signal(determining the mean value for defining the pixel position). Thecombination of all of these steps of the method according to theinvention supplies the required high resolution in determining theposition of marks. (When only a small resolution is required, individualsteps may optionally be omitted.) In addition, the working out of themethod by the relatively simple calculating operations is possible evenon small computer systems.

[0009] The invention will be explained in more detail below on the basisof embodiment examples shown at least partially in the Figures.

[0010] Here:

[0011]FIG. 1 shows a schematic representation of the arrangement of theinstrument for conducting the method,

[0012]FIG. 2a shows characteristic curve 6: Intensity distribution ofthe light reflected at the medium onto the receiver surface,

[0013]FIG. 2b shows the intensity distribution after removing theso-called dark curve (see below) from the characteristic curve 6,

[0014]FIG. 2c shows the curve of the intensity distribution of theso-called light curve (see below) after removing the dark curve,

[0015]FIG. 2d shows the curve of the normalized intensity distribution,

[0016]FIG. 3 is a representation for clarifying the determination of themark position (pixel no.) by evaluating different values of the measuredsignal (determining the mean value),

[0017]FIG. 4 shows a sketch for explaining the calculation procedure fordetermining the position of marks.

[0018] One variant of the embodiment of the method is demonstrated onthe example of the detection of a mark pattern in the signal curve of anoptical image.

[0019] One possible device for conducting the method according to theinvention is produced by a combination of light source 1 and alight-sensitive receiver 2 or receiver field (as a module), which arearranged over a reflecting scale 3 containing non-reflecting marks 4(see FIG. 1). The individual components are arranged such that thereflecting scale 3 is irradiated by light source 1 and the lightreflected at scale 3 is detected by receiver 2 or the receiver field. Bythis arrangement of elements, an optical image of the marks onreflecting scale 3 is assured by the light field 5 of light source 1 onthe light-sensitive receiver 2. The intensity curve reflected byreflecting scale 3 contains information in the form of signal troughs,which represent the position of marks 4 with respect to thelight-sensitive receiver 2. Thus, a significant intensity curve, whichis named characteristic curve 6 and which contains the positions of themarks, is formed in the receiver plane (see FIG. 2a).

[0020] The relative position of marks 4 in the receiver plane isdetermined from this intensity curve of characteristic curve 6 by meansof a special calculation procedure for the detection of marks.

[0021] These relative positions of the marks must now be transformedinto the absolute position of the marks 4 in the scale plane. As aprerequisite for working out the subsequent method steps, the knowledgeof the dark curve and the reference curve, which will be denoted thelight curve in the special case of detection of marks by means of anoptical detector, is necessary.

[0022] The dark curve represents the different dark signals produced byindividual types of detection on a light-sensitive receiver 2. It isthus recorded with a minimized measured signal—here the intensity of thereflected light; ideally the measured signal should be extinguished forthe plotting of the dark curve. These data are important, since therecorded intensity signals scatter due to the different transformationproperties of light-sensitive receiver 2 or the receiver lines. The darkcurve thus describes the offset behavior of the receiver 2.

[0023] Another correction of characteristic curve 6 must be conducted asa function of light source 1. For example, if the reflecting metal scale3 is illuminated with a punctiform light source 1, then the beam patternreflected back onto the light-sensitive receiver 2 or the receiver linesis characterized by the divergence of the beam bundle or the distancebetween light source 1, metal scale 3 and receiver 2. This [pattern] canbe recognized at the edge cutoff of the received signals. The lightcurve thus contains the intensity curve in the receiver plane withoutnon-reflecting marks 4. This curve is determined by the beamcharacteristic of the emitter, the receiving properties (to transformlight into an electrical signal), the reflection properties of scale 3and the marks.

[0024] In order to optimize the evaluation of the determined measuredvalues, which are represented by the characteristic curve 6, anormalization is required. This is achieved by subtracting the darkcurve from the intensity curve of characteristic curve 6. The result—thecharacteristic curve minus the dark curve—is shown in FIG. 2b. Now thedark curve is also subtracted from the light curve, which gives as aresult the light curve minus the dark curve (FIG. 2c); then thepreviously determined characteristic curve minus the dark curve isdivided by the light curve minus the dark curve and a curve is formed(see FIG. 2d), which permits the evaluation of the measured values, incontrast to the untreated characteristic curve 6. This normalized curveserves as a basis for the following determination of the relativeposition of marks in the receiver plane.

[0025] For this purpose, the points of intersection with the normalizedintensity curve are determined in specific reference planes which areset for pregiven intensity values by the course of the normalized curve(see FIG. 3). The pixels of the receiver plane are used as a measure forthe relative position of marks for this example of embodiment. The meanof all pixel values of the points of intersection yields the markposition in the receiver plane for one mark 4.

[0026] Finally, in conjunction with the method according to theinvention, the conversion results in the precise absolute position ofmark 4 in the plane of the scale. A transformation of the position ofthe marks results due to the projection of the mark patterns in thereceiver plane. However, this can be corrected.

[0027] From the knowledge of the distance Z₂ between the receiver planeand scale 3, the position x of mark 4 is determined from the markposition y in the receiver plane via the beam relative to theperpendicular line from light source 1 to scale 3 (see FIG. 4). Thus,the calculation procedure is simplified to:

x=y*z ₁/(z1+z2).

[0028] In order to optionally convey further information, in addition tothe absolute position of the marks, the marks could also be structuredin the form of a barcode.

[0029] The invention is not limited to the embodiment examples presentedhere. Rather, it is possible to produce additional embodiment variantsby combination and modification of the named means and features withoutleaving the scope of the invention.

List of Reference Numbers

[0030]1. Light source

[0031]2. Light-sensitive receiver

[0032]3. Reflecting scale

[0033]4. Non-reflecting mark

[0034]5. Beam field

[0035]6. Characteristic curve

1. A method for the highly precise determination of the position of amark pattern in a measured signal obtained by optical sensors for thedetection of marks on a scale, wherein data supplied by the opticalsensors with a minimized or extinguished measured signal are recordedand stored as a dark curve, the data of a normalized measured signal arerecorded and stored as a reference curve, the data of the currentmeasurement are recorded and are stored as a characteristic curve, andthen the characteristic curve is purged of errors caused by themeasuring instrument by comparison with the dark curve and/or thereference curve and/or is normalized, the thus-treated characteristiccurve is stored as the target curve, is hereby characterized in thatmarks are used for the labeling of the scale and the measured signal isevaluated by determining the points of intersection of the target curvewith the intensity levels determined by the intensity values forintensity values of the target curve that can be given in advance, andforming a mean value representing the position of a mark pattern fromthe determined points of intersection or combining the determinedintersection points into groups and then forming a mean valuerepresenting the position of a mark pattern for each group from theintersection points belonging thereto.
 2. The method according to claim1, further characterized in that the purging of errors caused by themeasuring instrument is conducted by subtracting the dark curve from thecharacteristic curve.
 3. The method according to one of claims 1 to 2,further characterized in that the normalization is conducted by formingthe quotient from the characteristic curve purged of errors caused bythe measuring instrument and the reference curve.
 4. The methodaccording to one of claims 1 to 2, further characterized in that fromthe position of mean values representing a mark pattern absolute markpositions x referred to the perpendicular line erected from the lightsource to the scale are calculated according to x=y*z ₁/(z ₁ +z ₂),wherein y describes the mark position in the receiver plane referred tothe perpendicular line erected from the light source to the scale, z₁describes the distance between the scale and light source and z₂describes the distance between the receiver plane and the scale.
 5. Themethod according to one of claims 1 to 2, further characterized in thata reflecting scale and a non-reflecting mark are used.
 6. An arrangementwith at least one processor, which is aligned such that a method for thehighly precise determination of the position of a mark pattern in ameasured signal obtained by optical sensors can be conducted accordingto one of claims 1 to
 2. 7. The arrangement according to claim 6,further characterized in that at least one light source, at least onelight-sensitive receiver and a reflecting scale are arranged such thatthe reflecting scale can be irradiated from the at least one lightsource and the light reflected at the reflecting scale can be detectedby the at least one receiver.
 8. The arrangement according to claim 6,further characterized in that the reflecting scale has non-reflectingmarks.